This invention relates to an apparatus for precisely measuring the length of an elongate product such as a rolled steel rod or shape or another elongate metal product.
It is known to position or to move such a product in front of a measuring apparatus, for example on a roller conveyor. The measuring apparatus has heretofore been of complicated structure or has given measurements of poor accuracy, or has had both types of drawbacks. The known devices include a fixed cell apparatus, which requires the product to be displaced at a uniform speed, and on optical circular sweeping apparatus, which brings about an error in trigonometrical angle measurements, this error increasing with the speed of displacement of the product. It has also been proposed to use optical fiber apparatus, having photosensitive elements at regular intervals; this type of apparatus has been expensive owing to the number of detection components required in connection with its data processing system; moreover, the length error has been of the order of an entire interval between two photo-sensitive elements. Purely mechanical devices have also been known to have been of very limited operating speed.
An object of the invention is to provide an improved apparatus, free of the drawbacks of the existing types of apparatus.